Typically, so called crossover buttons of the general type disclosed in the Douglas U.S. Pat. No. 2,618,166 have been employed to return the balls in the adjacent turns of the raceway when the length of the raceway is slightly less than one helical turn of the complementary grooves in the nut and screw. Buttons or guides of the type disclosed in the Douglas patent have comprised substantially U-shaped liners inserted into an aperture provided through the nut wall to lie wholly within the confines of the nut wall, and have incorporated deflecting elements which extend to deflect the balls into the liner. Such liners or guides have further incorporated projections extending from opposite sides of the guide which are positioned wholly within the groove in the nut to hold the guide in position so that deflection of the balls into and out of the channel can occur.
In addition to the foregoing patents which I incorporate herein by reference, load path inserts are in use in the industry which are assembled in the nut and have oppositely extending ball deflector legs for nuts with external ball return tubes. Such deflector legs extend into the groove in the screw to provide what is termed load path redundancy. Should all bearing balls be lost, the nut, for instance, will not free wheel to permit damage to the machinery which is being operated by the ball screw and nut assemblies. For example, when the ball screw and nut assembly is being used in a jack and a load is being supported, the load path redundancy inserts act like acme threads to prevent the nut or screw from free wheeling and the load from dropping rapidly due to gravitational forces. In some cases, as disclosed in the Galonska et al U.S. Pat. No. 2,995,948, deflector springs in the form of wire coil elements have been utilized. During normal operation these inserts, which have a cross section slightly smaller than the bearing ball diameter, are allowed to float radially and axially. Where extreme reliability is required, such as in aerospace applications, multiple redundant load path inserts are used in each ball screw assembly.